1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to methods and apparatuses for transmitting and receiving a preamble for multiple channel estimation in an Ultra-WideBand (UWB) wireless communication system.
2. Related Art
The existing narrow band multiple access method has a limit in performing multimedia high-speed data wireless transmission. Accordingly, there is a lot of interest in UWB communication. UWB communication is technology for transmitting a very wide signal by using a short radio frequency pulse of a nanosecond or lower. A UWB communication system may be defined as a system having a frequency band whose center frequency is 20% or higher or whose bandwidth is 500 MHz or higher.
A preamble for channel estimation may be used in a UWB communication system. The preamble is a previously agreed signal which is added to the front part of a data section, and is used for power control of the signal, frequency offset correction, and time offset correction. The preamble may be transmitted in a plurality of symbol periods, for example, a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols in the time domain. A channel estimation sequence is transmitted in some of the plurality of symbols.
A preamble, more particularly, a channel estimation sequence used in a UWB communication system requires a structure that may separate signals overlappingly received from the multiple antennas of a single relay terminal or from several relay terminals at the same time in order to enable the estimation of a UWB channel having a very large number of paths and improve reliability and the data rate. The simplest method of satisfying the requirement is to configure channel estimation sequences so that the sequences do not overlap in the time and frequency domains for each terminal. This method, however, is not preferred because the length of the channel estimation sequence is increased and frequency efficiency is deteriorated according to an increase in the number of relay terminals.
Meanwhile, a Space-Time Block Code (STBC) which may be used to estimate a channel in a multiple antenna system is basically designed such that codes transmitted for each antenna are orthogonal to each other in order to separate signals transmitted at the same time from the channel. Accordingly, a channel may be estimated without waste of frequency by using an STBC-based channel estimation sequence even in a cooperative communication environment including a plurality of relay terminals. This common channel estimation sequence, however, is problematic in that channel estimation performance is deteriorated because interference is generated between symbols if the number of multiple paths is many as in a UWB channel.
Accordingly, there is a need for a method and apparatus for transmitting a preamble including a channel estimation sequence, which are capable of improving the channel estimation ability of a system that performs transmission while performing frequency hopping, such as a UWB system, in an environment in which one relay terminal using multiple antennas or a plurality of relay terminal relays a signal through cooperation.